The present invention relates to a new and improved apparatus for and method of treating, especially finishing the surfaces of workpiece by means of a mass of smooth-surface or abrasive particles which impinge upon the workpiece surface.
Now, with a finishing method of this general character, typically known in the art under the term "sandblasting", abrasive particles are propelled at high velocity against the workpiece surface to be finished, for instance with the aid of a jet of compressed air. A modified version of this technique uses small pellets or spheres instead of the abrasive particles, these pellets or spheres likewise impinging at high velocity against the workpiece surface. In the last-considered procedure, instead of there being realized the sanding effect produced during sandblasting, a compression and to a certain extent smoothing of the workpiece surface is attained. In both procedures, one is actually concerned with a single-part production technique, the success of which is extensively dependent upon the dexterity of the party performing the work. Under these circumstances it is impossible to realize an economically interesting finishing operation, especially since the increase of the surface quality or fineness, possible only to a limited degree, requires a disproportional increase in the concomitant expenditure of time.
It is also already known in the art to use smooth-surface or abrasive particles during the finishing of workpiece surfaces in a manner different than the previously considered procedures. In particular, in this case the workpiece is embedded in a mass of such particles, the particle mass and the workpiece are then placed into revolving or vibratory motion. To this end, the particle mass and, as a general rule, a number of workpieces are introduced into a rotating vessel closed at both ends and possessing a substantially cylindrical or polygonal cross-section or into a vat-shaped container moved by one or a number of vibrators. Owing to the rotational or vibrational motion, the particles move along the workpiece surface, against which they are pressed by the pressure prevailing within the mass of particles and which is partially attributable to the force of gravity. The workpiece surfaces are correspondingly finished. Also in this case, however, there is a limitation upon the degree of fineness or finishing effect which can be realized within an economically feasible period of time, and just as was the case above, here also the required expenditure of time increases disproportionately with regard to the strived for surface finish quality or fineness. Furthermore, the manipulative steps, namely the filling and emptying of the vessels or containers, is extremely cumbersome and time-consuming, necessitating interruption in production.
Attempts have already been made to bring about a flow of material in vats moved by vibrators. But here also quite a considerable expenditure of equipment is required, especially since this objective only can be realized by complicated multidimensional vibrational motions of the vat housing the particle mass and the workpieces. The specific characteristic of such movements, as for instance path of motion and frequency, are dependent upon the properties of the particle mass and the workpieces. The flow of material which can be realized with this technique is accordingly relatively slow; any attempt to force production causing damage to the workpieces or to poor finish. Moreover, the flow velocity and thus the treatment time for the individual workpieces varies within wide ranges, so that the actually obtained degree of surface finish for a number of workpieces markedly fluctuates. Notwithstanding the flow of material, it is of course to be appreciated that periodic emptying and flushing of the vat cannot be avoided. The treatment of workpieces in vat-like containers which are subjected to shaking or jarring additionally requires a pre-treatment, for instance pickling, oftentimes however also a post-treatment of the workpiece surfaces, and thus brings with it a concomitant problem, the expensive problem of sewage disposal.